Protein or peptide engineering has recently emerged as a powerful technique as it holds great potential to be used in the fields of biomaterials and biotechnology. Also this technique is expected to have a great market ripple effect as it is applicable to various industrial areas such as development of new medicine, medical engineering and even for national defense industries. Biosynthetic proteins can have advantages over natural proteins in terms of the size, stability, and solubility, and possess a useful functionality that does not exist in human body. Therefore extensive effort has been carried out to develop a self-assembled structure with synthetic peptide or protein, and utilizing nano materials as a scaffold for constructing nano structure with bio soft materials such as DNA, protein, lipids, and amphiphilic peptide is continuously investigated worldwide.
Multifunctional polymer hydrogel is actively studied in various fields such as drug delivery system, bio-sensor, tissue engineering, and micro total analysis system, and its scope of application these days is not just limited in biomedical field, but widening even further. However, most of hydrogel used is based on polymers because hydrogel to be used as a biomaterial is necessary to fulfill critical criteria such as high moisture contents, adjustable viscoelasticity, injectability, and biocompatibility of not causing inflammatory responses when contacting a biological tissue, blood, or body fluid. Hence utilizing protein or peptide as a material for biocompatible hydrogel is being extensively investigated and modification in the peptide or protein sequences is introduced to improve their functionalities of the hydrogel. However, despite of these efforts, current bio soft material based hydrogel is still insufficient to be fully utilized in various area.
So far, types of hydrogel based on natural proteins such as elastin, collagen, gelatin, and globular protein, biosynthetic polypeptide-based hydrogels such as collagen-based synthetic hydrogel, elastin-like polypeptides, silk-elastin-like polypeptide, and coiled-coil motif-based hydrogel, hydrogels using peptides that form beta-pleated-sheets, oligopeptide hydrogels such as amphipathic peptide, multidomain peptide, and hybrid hydrogels combined with polymer are being utilized as biomaterials in development of hydrogels.
However, protein based hydrogel is susceptible to be degraded by proteases residing in living body and therefore increasing biostabiliy and sustainability of such hydrogel is remained as major challenge in developing protein based hydrogel. β-amino acid has been received intensive attention because it is unrecognizable by proteases. There have been a number of reports on a supermolecular hydrogel with self-assembling α-amino acid and β-amino acid with proteolytic stability (Zhimou Yang et al., Small 2007, 3, No. 4, 558-562). A Korean university research team developed a dynamic polypeptide hydrogel which responses to external stimulus and succeeded in forming a self-assembling dynamic polypeptide hydrogel through environment stimulus (Taek Gyoung Kim et al., Ad. Funct. Mater. 2012, 22, 2446-2468).
Furthermore, a recent patent (WO2010/045342) addressed that biostability of a protein is improved by exchanging some α-amino acids of a protein with β-amino acid. In the above patent, about 14% to 50% of α-amino acid residues found in a biologically active polypeptide or fragment are substituted with β-amino acid, and the remained α-amino acid residues were distributed in a repetitive pattern which resulted in improved biostability of the protein.
However, developing a hydrogel with a perfect biostability and biocompatibility is still impeded with critical hindrances, and biocompatible protein gel or biocompatible conductive protein gel that has technical significance in terms of biomaterial has not been developed yet.